Abstract

Introduction: The risk of mortality from cardiovascular disease (CVD) is higher in wintertime throughout the world, but it is not known if this reflects annual changes in diet or lifestyle, or an endogenous photoperiodic mechanism that is sensitive to changes in day length.Methods: Phenotypic data on cardiometabolic and lifestyle factors were collected throughout a 4 year time period from 502,642 middle-aged participants in UK Biobank. To assess the impact of seasonal environmental changes on cardiovascular risk factors, we linked these data to the outdoor temperature and day length at the time of assessment. Self-reported information on physical activity, diet and disease status were used to adjust for confounding factors related to health and lifestyle.Results: Mortality related to CVD was higher in winter, as were risk factors for this condition including blood pressure, markers of inflammation and body mass index (BMI). These seasonal rhythms were significantly related to day length after adjustment for other factors that might affect seasonality including physical activity, diet and outdoor temperature.Conclusions: The risk of CVD may be modulated by day length at temperate latitudes, and the implications of seasonality should be considered in all studies of human cardiometabolic health.Key messagesIn this cross-sectional study in UK Biobank, we report annual variations in cardiovascular risk factors and mortality that were associated with day length independent of environmental and lifestyle factors.These seasonal changes in day length might contribute to annual patterns in cardiovascular disease and mortality.